Prior work has established the advantages of orthogonal CDMA (OCDMA) over the more conventional quasi-orthogonal CDMA (QOCDMA) which is often referred to as asynchronous CDMA. OCDMA advantages stem from the fact that it has virtually no access noise and, thus, can support a greater number of users and is much less sensitive to power control errors. An OCDMA system is described in U.S. patent application Ser. No. 980,957 (which is incorporated herein by reference). As an example system a wireless PBX application was used. In this example, which used the ISM bands, it was possible to use time-division duplexing (TDD) which readily permitted certain time synchronization signals to be sent in a time-slot dedicated to their exclusive use. Thus, it was possible to easily obtain the timing necessary to operate an OCDMA system.
There are many bands in which it is not possible to use TDD and one must use frequency-division duplexing (FDD). In such cases, for several reasons one may not wish to use a separate dedicated time slot for timing signals. However, it is still necessary to derive and maintain accurate receive timing at the subscriber terminals. The object of this invention is to provide a novel technique for achieving accurate receive timing at subscriber terminals operating in an OCDMA system.